Ceramic process



' July-15,1952";

G- A- BoLe" csamrc raocsssj rind Get. 28, 1949'" PREF'ARATION OF ASJBSTANRALLY sou Gl-lUNG soumoa OFA GELABLE cowouxa m SUlTABLEcoxczn'rmnon mo HAVING THE ALKIaUNITY or THE soumon AoJusTEn TO Asurmau-z wow G'ELLING SLIGHTLY ALKAUNE H cERAmc' wrm MORE ACIDIG PH iATTA! N MIXTURE mo P R'nAL usumauzmo-u OF THE .GELA'SLE COHPOUHD To A PH0F ABOUT 7.5

GELAT: O N

m sn'u 1N MOLD REMOVAL Fsou mow AND names AND smems GECRGE A. SOLE!NVENTOR ATTORNEY MATERIALS 1 Mi y il b re 5 t fipf v i r t 5 methodspreyicgsly used-jar tl 1e manufaqture01 nlglded ceramic products Theseimprovements l ul nu nu a mr neme yfiuc Pr ins, concentration of sil a(S1051 het'weep gbcgti 15- occur; btlt such thzit nei erthelee's'whehthe "sow;

and gnother'ct which is acemmic material eh'q' providei'i 'I controlspbstentially" Cel'ti 45 ranges, the' concentration of the' gelling00;!!- pouhdf a'rxd tl'iypH olfthefmlxtur, forzzfrly' secure e"geillih'g' cfazzl'ic' progluct yghigh; has. a. commercially? workble'non gr-anular stmc'turi I. -50 lt isikh'uvm that certair claizpeterialsreaetjg with P 'e' l to fare: wm l aelcat reI d Pi ?P h l l mce slim i te with another base. when ajproper cqpcentra tlon at a,sodium silicate solution reacts with an '65 raise-413* 1 acid undercertain. conditions, thesolutiors comegels. The time period of thisgelation depends largely upon the concentration, temperature and acidityor alkalinity ofthe gelling solu-L; f tion (1. e. the pH cf thesolution'h .At a IIH 1: near nettrality the gelatio'nct si ch ajsalution maycccur quickly but at higher pH values; the r time is longer andat low pH values the have discovered-that anon-granular gelled ceramicstructure may be formed in situ in amolci by (1) preparing a liquidbatchwhich' ccinj sistsof a water-solution of a. water soluble sill;cate, the latter being partially neutralized tc; 1a" pH wl-lich is just-above the rapid gelling point.- by the addition of anacid or an.acldwsalt and? (21' adding a dry or, liquid ceramic batch to'the liquidsilicate batch, the ceramic hatch being more acidic than the silicatesolution a'ndusually' being ctu lt dim r 1,' hercj point out that thereare definitere fedlimits for the pH of the mixln order to sec'iresatisfactory results and-not only'ls a contxiql ci the p H necessary.butalso a control of the" cqncegtratiozrgoi, the. gelling agent is'necessary and. thattlge degree or concentration modifies the lingritsoithefnecesser-ypH. Thelimitatiofis on the range cf conditions cf the mixare very -1 I ha.ve fgu r d thax ii I precondition a. silicate solytionto prigg it toja 'pr'oper conditioner sill cete cphgepfcretipz'r andhydrogen ion corlce,x:ltra.-'- tiprrgpcljhen mixyrith the ceramicmaterial a;1'd lwme gel to 01m irrsitu m 'a'rnold; 1 elim- Z inate thecracking and spoilage difficulties.

flfnus',-to recapitulate, I may' point out there} rejhree ways er addingthe'pH conditioner (in? my prccess. the conditloner'islan ecldlz 1) Aterthe mixture of ceramic material and elling agentp V v (d?) To theceramic'materlal-betore (31' To the gelling aer'ztbeforemmure." j e Ihave found that the last method is most a,dvantae oz-is because therebyI can revent gram;- f lar format-ion and consequei'it cracking and als ci I camin connection.- tlierewlth, by proper c'qni 11:01 also ofthe'ccncentratien of the gelling com-" peund elso control the time ofgelation, 1n some m odiment 10f my' rocess', I amp a jglff tlonadvantageous. In other emho'diments,y 1

prefer to have the gelatlon proceed' more slowly.Foqexfa-mplgwhere'aconvyor is used to' transport the f lled moldsto adrying furnace, it desirable that the gelling time shall substantially'.-m-'-- 1;. j v; L y H .1 I ;-----UNITED STATES PATENTH -QQFFI'CE;;1;*,

' were so scant oral; i: Dhlo State Uni'versiti' Research Foundation. 1I Coltx'nb'u's, Qhic, -a,corporgtlan at Ohio y time the mold is on the fveyor. I control the time or gelation by control-- of the concentrationand of the Inthedrawingn,

{ The figure is aflow sheet illustrating a process performed.in'ac'cordance with my invention.-

lcererring especiallyto-the figure of the drawme it may be noticed thatthe first step illustrated as comingunder my invention is thepreparation of a substantially non-gelling solution or a gelablecompound iii-suitable concentration, gand having the alkalinityof thesolution a.d' dusted to a suitable non-gelling slightly alkaline pH. 'Afurther step comprises the mixing 0! this:

: adjusted gelable solution with the ceramic ma-' terlal for which ithas been adjusted, the ceramic material having a more acidic pH than thesolu jtlon so that the mixture is partially neutralized to obtain a pHwhich is slightly alkaline but within the relatively quick gellingnon-granular forming range. The mixing might take place in the mold butpreferably the materials are mixed outside of the mold and the mixtureis poured into a mold where gelation occurs relatively rapidly.Thereafter, the product is re moved from the mold,.dried in a dryingoven.

and baked'in a oven. Although I prefer first to form the solution of thegelable compound by thoroughly dissolving .ej silicate in an adeq uatequantity of water and thereafter to adjust the solution to the desiredtime the molded product becomes still and can be removed from the moldand placed in the drying and baking ovens where it and quality and d ieble'characteristics.

Although other soluble silicates than sodium silicate are usableas willlac-explained hereafter;

yet sodium silicate is probably the cheapest nowavailable andinillustrating the desired concenbaked to mm. finished ceramic product armiration'oi, solute and-dezrceof alkalinity,'it- 18. v

'c'onvenient torefer to solutions of sodium silipH of a water glasssolution increases with increasing concentration or the silicateAlthough pure water is substantially neutral, and very smallconcentrations '01 sodium silicate in water are also substantiallyneutral, the alkalinity of a solution increases with increasedconcentration of the sodium silicate until, for excurs unless there isan excessively high concen-f traticn and so long as the pH oi thesolution is degree of alkalinity for mixing with the ceramic ;materialin question, yet it is wholly possible to v example, I may dissolvesodium silicate in a gelling solutionof the gelable compound may lieanywhere between 8.0 and 10.0 or perhaps higher or lower? In theperformance o! my process I usually prefer that the'adjusted pH liee'process; ;'ihe two steps may-be considered elling solution of a,gelablecompound in suitalkaline pH. ;V.Thereaiter, the solution is mixedwith'the ceramic material. which ha a more on which is slightly alkalinebut is not In removed from a neutral solution,

i'mixture or the silicate solution and the ceramic the silicate being insuitable concen-' obtain the same result in different ways. For

suitably diluted solution of sulfuric acid-the.

mixture may vary and depends on the acidity of the ceramic materialwhich is to be added thereto.- The operable pH value oi the adjusted nonas the single step of preparing an adjusted nonacidic pH. so that themixture attains a gelling.

ample, a sodium silicate'solutlon with the concentration developed byadding about 80 cc. of a 24.5% Sit): sodium silicate solution to 1000cc. of water has a pH of about 11.0. Moreover, I

' have found that while an unadjusted solution 0! sodium silicate havinga very low concentration not gel substantially under any circumstancesand even as the concen ration of water glass in the solution. increases,no gelation ordinarily onnot adiusted as for example by the addition-o1other substances, nevertheless, the pH is 'duced by acidifying thesolution, 'suchsolution will gel at a. iairly definite alkaline range(de- Iv pendent on its concentration) as the solution appreaches aneutral alkalinity. Moreover, I have between 8.0 and 9.0. These limitsare not crlti but are furnished as an aid in performingble concentrationwith a suitable non-gelling I prefer a pH of about 7.5 in the set gelwhich; is thus the preierr'ed pH factor "oi the complete round that thebreadth of the gelation range measured on the pH scale increases as thecon-' i centration increases, but that at the same time, I the tendencyor the solution to become granularquickly during the gelation processalso increases as the concentration of the solution is increased. Iprefer a concenn-atio of SiO: in the silicate solution of betwesn'OfTSand 2.4%.

By this I do not mean that any solution with-' in the above mentionedlimits of concentration may be satisfactorily gelled at any point withinthe above mentioned limits of pH. For instance,

the satisfactory range of pH values correspond-" ing to a concentrationor 0.75% is relatively nar--' row. It is also relatively low having arange about as broad as 0.01 at a pH value of about 7.2

as, for example, extending from 7.195 to 7.205. On the other hand, thesatisfactory range 011 pH values for a. solution having a concentration.1121 from 2.0% to 2.3% is relatively broad extending from about 7.3 toabout 7.9. Concentrations of about 2.2% and higher have a very. short5818-; tion period. Because of the narrow range at lovv'j, vconcentrations and because of the very rapid -,gelation in the higherconcentrations and the possibilities otaccidental crystal Iormationln'such higher concentrations, I usually prefer to operate in aconcentration range of from 1.2% to 2.1% and to cause gel formationthereonat a l pH value of from about 7.3 to about 7.8.

tration However, a yeriation of a few tenths I in the pH factor does notprevent the proper operation according to myimnroved process. I itslater explained, I usually operate in the range between 7.2 and 7.9,

The cornpletengijwe of silicate and iceramic material ispoured in a.

a W x a: e mold and is allowedfto gel in the mold performance of theprocess but is-no more lm-i portant than the lira-it's of pH valuesmentioned.; I may use any suitable gelling compound. For

The concentration of SiO: is important in the instance, any of thesoluble silicates including the alkali silicates such as.

sodium and lithium silicate may be used; an e so uble alkyl silicatessuch as, for ex- Inga short ample, ethyl silicate, are usable althoughsome;

assium silicates tory' product 7 moved. drledandflredintheusual mannerproduce the ceramic; products desired.

The ceramic material may be of many kinds.

Thus. Ohio fire c183: 1m southern Ohio. Iowcr Kittanni'ng fife clays.Thomas Alabama fire clays. Ohio shale and silt. and mi; have been used.Also, I have used various clays from Stark County, Ohio; Olive Hill,Kentucky:' irom Georgia: northern Illinois: and from As is stated above,sawdust may be mixed with'clay and I have used both hardwood sawdustsand soft- Example I A liquid batch. was prepared by adding .150 ofsilica I soda brand) to 2700 of water. This solution, having a pH of 10when iornied was partially neutralized to a pH of 8.5 by the additionthereto oi 12 cc. of concentrated sulfuric acid.

A dry-batch was formed separately by mixing 2100 grains of raw cvanite(lQQmesh) plus 1500 grams of Thomas abama firefly (pH 8.05) and 600grands of softwood sawdust (pH 5.5) (20 mesh-Tyler screen) The drybatchwas introduced slowly with continuous stirring into a receptaclecontaining the liquid batch untila uniform mixtm'e was obtained.Apprommately five minutes was required for the operation. Thrnixture wastransferred to a metal mold and allowed to stand for fifteen minutes.During this time the p-H of the batch gradually decreased toapproximately 7.5.

, 8 to form-2000 grams of havihgatemxieratureolfiliandapflofll),

when forr'ned was partially neutralized to a 1:30!

8.40 by the addition thereto or 108 cc. 0! a soldtion containing 1 0% oisulfuric acid. s. g. 1.8.

A dry batch was formed separately 131m. 1600 grams of No.5 LowerKittanningflre my (-35 mesh, pH 6.28) and ce grams or softwoodsawdustl-ZSmeshmKLW). L .The dry batohwas introduced slowly withcontinuous stirring into a receptacle-containing the liquid batch untila. uniform mixture was obtained. After iorthree minutes the ruin-- turewas out in a metal mold and allowed to stand for twelve minutes. The pHof the mix} ture decreased to 7.86 and set to a self supportingnon-granular gel in ten minutes. After an elapsedtiz ne oifiiteenminntesiroin starting to tion, having a temperature of 82" F. anda. pH

The self-supporting, non-granular gel structure so formed wastransferrcdirom the mold to a drier maintained at a temperature of 220F. and

dried. The, ceramic block was dried without sub-' stantial shrinkage andwithout cracking. The block was then subjected to high temperature Aliquid batch grams of sodium silicate ("S" special brand) to 2090 gramsof water. This solution having a temperature of 76 F. and a pH of 10.78when formed was partially neutralized to a p3 of 9.32 by the additionthereto of 7 cc. of sulfuric acid 5.3.1.84.

, A dry batch was formed separately by mixing 2000 grass oiraw ky nite(290 mesh), pH 5.05 plus 1036 grams of Thomas Alabama fire clay (pH3.67) plus 150 grams 0! calcined gun-nine. and 200 grams of softwoodsawdust (-28+IUI) mesh), pH 5.0.

The dry batch was introduced slowly with contlnuous stirring into areceptacle ccntating the liquid batch until a uniform mixt'me wasobtained. After mining for three m nut themixcure was cast in a metalmold and allowed to stand for twelve minutes. The pH of the mixturedecreased to 7.62 and after nine minutes, set to a sellsupporting,non-gran" gel structure. after an elapsed time of fifteen m nutes fromstarting to mix, the unit was tension-ed from the mold to adrier,meintanned at a temperature of 200 F. and dried. The unit, which driedwithout cracking, was then subjected to hlgh temperature kiln tiring. Itwas a satisfactory low weight retrac- T shin le in A liquid batch wasprepared by dissolving 150 grams of sodium si1icate ("0" brand) in wasprepared by adding 150' oi l0.7 9 when formed, was partially neutralizedto a pH of 8.40 by the addition thereto 01 333 cc. of a. solutioncontaining 10% of sulfuric acid, 5. g. 1.84.

A dry bath was formed separately by.mixing. 1000 grams 01 No. 5 LowerKittanning hie clay (-dglrnesh, pH 6.28) and 503 grams of groun gig;{-400 mesh, PH 6.99). The-dry batch was then added slowly to the liquidbatch and mixed thoroughly until a'uniicrm mixture was-obtained. Gaspockets were formed by a foaming process. Alter mixing a total of oneminute and fortyfive seconds the mixture cast in a. metal mold andallowed to stand for ten minutes. or the mixture decreased to 7.80 andit set to 8.

' self-supporting non-granular gel in eight minperature kiln firing. Itwas a satisfactory low weight structural product.

It is to be understood that the above described embodiments of myinvention are for the purpose oi illustration only and various changesmay be made therein without departing from the spirit and scope of theinvention. 1

I claim: 7

1. In a method 01 making ceramic products, the steps which compriseionnin'g a solution of a soluble silicate in water; the pH value or saidsolution by introducing therein an acid reagent in quantities ins; cientto efiect rapid .-:ea1ter, but before the solution has relied, ceramicmaterials selected from the class of ceramic materials consisting ofclays, silts, shales and kyanites having an acid-reacting character intothe solution to;

form a slurry in quantities sufficient-to create apH value, of theslurry a range suhstantzally of from 7.2 to 7.9 and casting'the slurryin a mold. 7 2. A method of making a ceramic. product. comprising thesteps or producing a solution Samoan. "rm; solution The pH- aooawoducins an acid reagent into said solution in quantitles to cause thesame to acquire a pH value.

intermediate that of a normal solutioncf the silicate in water, and 'asolution which"wlll'rapid l! gel; thereafter-[burl before the solutionhas 1n gelled, mixing into said solution anacid-reactinz' 'ceramicmaterial selected from the clas cos ramic'materials consistin: or clays,silts', shales and kyanites to form. a'slurry having a pH of about 7.2to 7.9 and introducingth slurry into a mold, whereby a gel formsandstificns to set the slurry to cause it to assume a stiff and set-upcondition. a

3. In a method of making ceramic products. the steps which compriseformic;- a dilute solution of a soluble silicate in water having had the153 value of said solution reduced from the pH value of a normalsolution by the presence of an acid reagent in quantities insufficienttoeflect rapid gelation of the solution; thereafter, but before thesolution has gelled, mixing clay into the solution to form a slurry; andcasting the slurry into a mold, the claybeing of an acidreactingcharacter when in aqueous solution and being present in the slurry inquantities suficient to create a pH value in the slurry when cast atabout 7.5. 4. The method of making alight weight ceramic refractorywhich comprises forming of a non-gelling water solution of a watersoluble silicate, having said solution partially neutralized to an'on-gellin slightly alkaline pH; forming a dry mixture composed o5 clayand'a finely divided combustible cellulose material, said dry mixturebeing of an acidic ohara cter; mixing the drymixture with the ungelledsilicate solution to .form a slurry having a pH of about 7.2 to 7.9; andmolding the slurry, the acidic character of the ingredients comprisingthe dry mixture serving to effect further neutralization of the silicatesolution and a development of a gel in the slurry following the castingthereof.

5. The method of making ceramic refractories which comprises adding anacidic clay to a partially neutralized ungelled solution of a watersoluble silicate; and casting the resulting ,m-- turc.

6. A method of producing a ceramic product which comprises forming apartially neutralized dilute solution of a soluble silicate in water,the neutralization being insuificient to cause rapid gelation thereof;adding to said partially neutralmed solution before it has gelled, drymaterials in the form of an acid containing clay to form a mixturehaving a nil of 7.2 to 7.9; and casting the resulting mixture, thenaturally contained acids; present in the clay serving to effect fu.ther neutralization of the solution into a gelation range in order toform in situ in the. cast materials a mobile, non-granular uniformlydistributed gel.

7. The method of producing ceramic products which comprises forming adilute solution of a soluble silicate in water having a concentration ofS; in the silicate solution or'betu'een 0.75% and 2.4%; partiallyneutralizing said solution by the addition thereto 05 an acid reagent;adding to said partially neutralized solution before it suia tingmixture in a mold; retaining the mmt-ure' the clay and sald organicsubstance serve to elect further neutralization o! the solution formingmaterial-races to aehievea pHbetw'een7-3 L9; whereby to efiectdevelopment in said rials of a uniformly distl'iblltt HOD-mull: silicategel; following the setting 0! 8 d rials, the same from the mold and dryin; same; and thereafter firing the product athig'h mvcr hmc 8:1methowot a ceramic comprising the steps of producing a solution composedof a. soluble silicate in water having a. concentration of silica in thewater of from 1.2 to 2.1%; introducing an acid reagent into saidsolution in quantities to cause the same to assume a pH value of between8.0 and 9.0 but which does not at the concentration oi the sillcate insolution cause it. to form a gel rapidly; thereafter mixing saidsolution before it has gelled, with an acid-reacting ceramic materialselected from the class of ceramic materials consisting of clays, silts,shales and kyanites to form a slurry and tocause the slurry to acquire apH value between about'7.3 and 7.8; and then introducing the slurry intoa mold, whereby a gel gradually forms and stidens to set the slurry tocause it to assume a still and set-up condition.

9. A method of making a ceramic product; comprising the steps ofproducing a dilute solution composed of a. soluble silicate in water,having a concentration of silica in the water of from 0.75 to 2.4%;introducing an acidreagent into said solution in quantities to cause thesame to acquire a pH value or from 8.0 to 10.0 without prise producinga. dilute solution of a soluble silicate inwater; introducing saidsolution an,

in said mold for a. sufieie'nt period's; time so E that the naturallycontained acids present in:

neutralizing said solution surlicien'tl-y to cause the rapid formationof a gel; thereafter, before of the solution by introducing therein anacidv reagent in quantities suficient to create a. pH value within therange of from 8.0 to 10.0; thereafter mixing clay and a finely dividedsawdust into the ungehed solution to form a slurry; and casting theslurry in a mold, the clay and the Organic material being of anacid-reacting character when in aqueous sue ns-ion and being present inthe slurry in go ties suificient to create a pH value of slurry, whencast within the range of from 7.2 to 7.9.

11. In a, methodof making ceramic products,

the steps which cone-prise preparing a non-gelling dilute aqueoussolution of-a soluble silicate compound having the alk ty of saidsolution adjusted to anon-gelling s ghtly aI-ha'inepH value; mining clayinto the un lied solution toform a slurry; and Casting the surry in amold, the clay being of an acid-reacting character when in aqueoussuspension and being present in the slurry in quantities suificient. tocreate a pH value of the slurry when cast within-the range of from 7.2to 7.9.

12. In a method of forming a. light \re'mht cellular ceramic product,the steps which comacid; reagent in amounts necessary to artiallyneutralize the same without effecting rapid geial rials cbmprisi a thedry we; those m whenwetted serving to reduce the'pH value 0!.

- 12 p 14. An mterz nedlete product in the tormatinn O I wrfimic P t amolded Iorm' '0! a gelled non-crystalllne stxfuchxre eqnslstlng i 4 'ota mixture pl an ungelled solution formedtro'm 1 we uneelled silicatesolutlnn to produce a 5 a soluble slllcabe'and a cenunlc materialselected casting slurry; and; introducing the slurry into item the class0! ceramic materials consisting of I. mbld, theLacldlc character of thedry materials, Clays, silts, shales and mmtes, the mixt m mg a pH in therange between 7.2 and 7.9 and 3 the partially neutralized sqdlumsilicate-solution haying a concentration of frpm 0.75 to 2.4% at so thatth slurry eeduires after being cast in '10 510: to the mold, a; pHvellue 01' Iron; 7.2 to 7.9 whereby there is developed withinthe castmaterials, a mobile, non-granular eel.

13. An intermediate product in the formation 11. tlon then-:0; forming adry mixture compoeed of a finely divided acidic clay and a cembustlble Icellulose maperial; intimately the mate- GEORGEHA. Bqm 1 REFERENCES crrmThe followmg' references are of record in f c r prcduct comprising a.dried molded 15 me this patent; the

form of a gelled npn-crystallme structure con- UN STATES PA sistiz'lg ofa mixture of a solution of a soluble sili- .L cafe and a ceramicmaterial selected from the Number Name Date class-of ceramic materialsconsisting I of clays, 2,2 ,131 Barker et a1. Dec. 30, 1941 if: slits,shale'send kyanltes, the mixture having 20 2,318, 53 Carter .May 11,1943a pH in the range between 7.2 and 7.9. 2, 27,390 Blah]. Oct. 24, 1950

7. THE METHOD OF PRODUCING CERAMIC PRODUCTS WHICH COMPRISES FORMING ADILUTE SOLUTION OF A SOLUBLE SILICATE IN WATER HAVING A CONCENTRATION OFSIO2 IN THE SILICATE SOLUTION OF BETWEEN 0.75% AND 2.4%; PARTIALLYNEUTRALIZING SIAD SOLUTION BY THE ADDITION THERETO OF AN ACID REAGENT;ADDING TO SAID PARTIALLY NEUTRALIZED SOLUTION BEFORE IT HAS GELLED, DRYMATERIALS IN THE FORM OF AN ACID CONTAINING CLAY, KYANITE AND A FINELYDIVIDED COMBUSTIBLE CELLULOSE MATERIAL; CASTING THE RESULATING MIXTUREIN A MOLD; RETAINING THE MIXTURE IN SAID MOLD FOR A SUFFICIENT PERIOD OFTIME SO THAT THE NATURALLY CONTAINED ACIDS PRESENT IN THE CLAY AND SAIDORGANIC SUBSTANCE SERVE TO EFFECT FURTHER NUETRALIZATION OF TH ESOLUTIONFORMING MATERIALS SO AS TO ACHIEVE A PH BETWEEN 7.2 AND 7.9 WHEREBY TOEFFECT DEVELOPMENT IN SAID MATERIALS OF A UNIFORMLY DISTRIBUTED,NON-GRANULAR SILICATE GEL; FOLLOWING THE SETTING OF SAID MATERIALS,REMOVING THE SAME FROM THE MOLD AND DRYING THE SAME; AND THEREAFTERFIRING THE PRODUCT AT HIGH TEMPERATURE.